And before that, there was sound ranging!
It is difficult to locate a mortar position with sound. Mortars aren't that loud when they fire, and they can fire from deep defilade. Also, sound propagates slowly enough to give them critical seconds to "shoot and scoot". Even with radar, we would fire our 155s not only on their firing position, but also on likely routes of egress. The Iraqis had mortars mounted in the back of BMPs so they could move as quickly as possible after launching a volley, as well as having some armor to protect them from shrapnel while they were moving.